Method and apparatus for copy protection detection in a video signal

ABSTRACT

A method and apparatus for detecting copy protection included in an input video signal is described. Two types of copy protection are particularly addressed, including techniques that imbed copy protection pulses and copy protection phase flips in the video signal. A method for preserving copy protection is also presented, where the input video signal is first examined to determine if copy protection has been included in the input video signal. The input video signal then converted to component video data, which removes any copy protection present. An output video signal is then generated from the component video data, and when it was determined that the input video signal includes copy protection, the copy protection is recreated in the output video signal.

RELATED APPLICATIONS

This application is a divisional application of application Ser. No.09/316,442 entitled “Method and Apparatus for Copy Protection Detectionin a Video Signal”, having inventor Antonio Rinaldi, filed on May 21,1999, now U.S. Pat. No. 6,690,880, and owned by the instant assignee.This invention is related to the invention disclosed in a patentapplication entitled “Method and Apparatus for Processing Video SignalsHaving Associated Access Restriction Data”, U.S. Pat. No. 6,606,450,which was issued Aug. 12, 2003 and has a filing date of May 21, 1999.

TECHNICAL FIELD OF THE INVENTION

The invention relates generally to video signals, and more particularlyto detection of copy protection included in video signals.

BACKGROUND OF THE INVENTION

Video signals may originate from a number of different sources includinga videocassette recorder (VCR), digital video disc (DVD) player, etc. Inorder to prevent users from making unauthorized copies or derivations ofprotected works included in video signals, copy protection techniqueshave been developed that prevent such video signals from being recordedon standard recording devices such as VCRs. These copy protectiontechniques allow the signal to be utilized for display purposes, butprevent recording devices such as VCRs from accurately recording all ofthe information in the video stream.

As video graphics processing circuits continue to evolve, additionalcapabilities that allow video signals to be provided to a number ofdifferent outputs of the circuits exist. In such systems, the videosignals are often broken down into their component parts and stored inmemory. When video signals are broken down in such a manner, thetechniques utilized to implement copy protection in the video signal areoften defeated.

In some instances, the output data stream of the video processingcircuitry is not provided to a device capable of recording theinformation included in the video signal. In such instances, defeatingthe copy protection included in the video signal is not an issue.However, if the video signal is reconstructed from the component dataand provided to an output that may be connected to a VCR or otherrecording capable device, the video graphics circuitry has effectivelyremoved the copy protection from the video stream. As such, this allowsfor unauthorized copies or derivations to be produced, which isundesirable.

Therefore, a need exists for a method and apparatus that is able todetect copy protection included in a video graphics stream and ensurethat when it is present unauthorized copies or derivations ofinformation included in the video stream are not permitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flow diagram of a method for preserving copyprotection in an input video signal in accordance with the presentinvention;

FIG. 2 illustrates a flow diagram of a method for detecting copyprotection pulses in an input video signal in accordance with thepresent invention;

FIG. 3 illustrates a flow diagram of a method for detecting phase flipcopy protection in an input video signal in accordance with the presentinvention;

FIG. 4 illustrates a block diagram of a copy protection pulse detectioncircuit in accordance with the present invention;

FIG. 5 illustrates a more detailed view of the pulse detector of FIG. 4;

FIG. 6 illustrates a block diagram of a colorburst phase flip detectioncircuit in accordance with the present invention;

FIG. 7 illustrates a block diagram of a more detailed view of the phaseflip detection block of FIG. 6;

FIG. 8 illustrates a block diagram of a more detailed view of the fieldcounting block of FIG. 6; and

FIG. 9 illustrates a block diagram of a more detailed view of theinterval counting block of FIG. 6.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Generally, the present invention provides a method and apparatus fordetecting copy protection included in an input video signal. Two typesof copy protection are particularly addressed, including techniques thatimbed copy protection pulses and copy protection phase flips in thevideo signal. Techniques for detecting each of these two types of copyprotection are described. A method for preserving copy protection isalso presented, where the input video signal is first checked todetermine if copy protection has been included in the input videosignal. The input video signal then converted to component video data,which removes any copy protection present. An output video signal isthen generated from the component video data, and when it was determinedthat the input video signal includes copy protection, the copyprotection is recreated in the output video signal.

By allowing for copy protection included in video signals to bedetected, steps can be taken to ensure that the intent of the copyprotection is upheld. As such, if the input video signal is converted tocomponent video data and then provided to an output that may be coupledto a recording device, the copy protection included in the input signalcan be recreated in the output video stream. Similarly, in the casewhere a computer or other processing device can capture images withinthe input video stream, the presence of copy protection can cause theprocessor to disallow these image capturing functions that record orcopy portions of the video stream. By upholding the intent of the copyprotection included in the video stream, producers of copy protectedmaterials can be reassured that video graphics processing devicesdesigned to work with such media will not enable users to makeunauthorized copies or derivations of copy protected works.

The invention can be better understood with reference to FIGS. 1-9. FIG.1 illustrates a method for preserving copy protection in an input videosignal. The input video signal may be derived from a number of differentsources including, but not limited to, the output of a VCR, DVD player,or other playback or broadcast device that produces video signals thatmay be copy protected to ensure that unauthorized copies or derivationsare not produced.

At step 102, the input video signal is received. At step 104, it isdetermined whether or not the input video signal includes copyprotection. Step 104 may include a number of additional steps, which aredescribed in more detail with respect to FIGS. 2 and 3. FIGS. 2 and 3illustrate the techniques for detecting two specific types of copyprotection often included with video signals. The first type of copyprotection often included in video signal is pulses that are typicallyincluded in the vertical blanking interval of the video signal. Thesecond type of copy protection involves phase flips that are included inthe colorburst portion of certain sets of lines within the displayfield.

At step 106, the input video signal is converted to component videodata. This type of conversion is often provided such that the componentvideo data can be stored in memory on a video graphics integratedcircuit prior to recompiling the component data for output. When theinput video signal is converted to component video data, the copyprotection that may or may not be included within the input video signalis eliminated. This is because the copy protection included in the videosignal is typically in addition to the underlying video signal such thatthe data of the video signal can be separated from the copy protectionwithout disturbing or corrupting the data. The copy protection is oftenprovided in a way such that a television set or other simplistic displaydevice will not be affected by the inclusion of the copy protection,whereas recording devices such as VCRs will be unable to accuratelyrecord the underlying video data.

At step 108, an output video signal is generated from the componentvideo data. The output video signal may be provided to a television set,a display monitor, or to another video graphics integrated circuit foradditional processing. At step 110 a decision is made based on whetheror not it was determined that the input video signal includes copyprotection. If the input video signal is not copy protected, no furtheraction is required as there is no need to recreate any copy protection.However, it should be noted that rather than basing the inclusion ofcopy protection information in the output video stream on the presenceof it in the input video stream, other circuitry or software within thevideo graphics integrated circuit may control the addition or removal ofcopy protection from an input video signal. Thus, an unprotected inputvideo signal may be provided to the input of the video graphicsintegrated circuit and copy protection may be added to that signal priorto being provided as an output. Similarly, some type of override may beimplemented within the video graphics integrated circuit such thatalthough the copy protection present in the input video signal isnormally included in the output video signal, this state can beoverridden such that the copy protection is not included in the outputvideo signal. It should be obvious to one of ordinary skill in the artthat once the techniques for detecting the presence of copy protectionin an input video signal are derived, the uses for such detectiontechnology can vary with respect to the particular application.

If it is determined at step 110 that the input video signal includescopy protection, the method proceeds to step 112, where image capturingfunctionality within the video graphics controller is disabled. Thisstep ensures that image-capturing applications within devices such aspersonal computers are not used to capture portions or segments of theinput video stream. Thus, the video graphics processor would disallowMPEG, JPEG, or other files that include portions of the input videosignal from being created.

At step 114, it is determined whether or not the output video signal isprovided to a recordable output. In other words, it is determinedwhether or not the output video signal is being provided in such amanner that an external recording device could be coupled to receive theoutput video signal and record the information derived from the inputvideo signal. It should be noted that this step may be eliminated suchthat any copy protection present in the input video signal isautomatically included in all output versions of the input video signal.If step 114 is included, and it is determined that the output videosignal is provided to a non-recordable output such as a LCD displaydriver, the copy protection included in the input video signal is notrecreated in the output video signal.

If it is determined at step 114 that the output video signal is providedto a recordable output, such as a television out signal on a videographics circuit that may be coupled to the input of a VCR, the copyprotection is recreated at step 116 in the output video signal. Therecreation of the copy protection prevents recording of information inthe output video signal derived from the input video signal. Thus, themethod of FIG. 1 determines whether or not copy protection has beenincluded on an input signal, and when it is present, it is recreated inoutput signals derived from the input signal when those output signalsmay be subject to recording.

FIG. 2 illustrates a method for detecting copy protection pulses in aninput video signal. The method of FIG. 2 may be utilized at step 104 ofFIG. 1 to determine if the input video signal includes this type of copyprotection. The method of FIG. 2 begins at step 202 where the inputvideo signal is quantized, or digitized, to produce a digital videosignal that includes a stream of values. Each of the values within thestream represents a quantized portion of the input video signal.

At step 204, each of the values in the digital video signal isindividually compared with a first threshold. Preferably, the comparisonof the values in the stream with the first threshold occurs in a serialmanner. In the preferred embodiment, the first threshold is a verticalblanking interval peak white threshold, and the comparison at step 204is performed to determine if automatic gain control pulses within theinput video signal exceed the vertical blanking interval peak whitethreshold. The amplitude of the portion of the input video stream iscompared with this threshold in order to determine if it has beenexceeded.

If it is determined at step 204 that the first threshold is not exceededby the portion of the input video stream, the method proceeds to step206 where the next value of the input video stream is prepared forcomparison. If it is determined at step 204 that the value does exceedthe threshold, the method proceeds to step 208 where an accumulatorvalue is incremented. At step 210, it is determined whether or not theend of a display field has been reached. If not, steps 204-208 continueto be executed with subsequent values in the input video stream. Thus,steps 204-210 effectively count the number of pulses, or values includedin each display field that exceed the first threshold, which ispreferably the vertical blanking interval peak white threshold. Theaccumulator value is cleared at the end of each frame.

In the form of copy protection that may be included in an input videosignal that this technique is attempting to detect, a certain number ofautomatic gain control (AGC) pulses are included in each display fieldof the input video stream. These pulses prevent videocassette recordersand other similar recording devices from effectively recording theinformation in the input video stream. Such pulses are often varied, orpulsated, from field to field such that their amplitude changes from onefield to the next. As such, in some fields the pulses may not exceed thefirst threshold, whereas in other fields the threshold will be exceeded.

In order to ensure that the detection circuitry does not continuallyswitch back and forth from the states of detecting and not detecting thepresence of the AGC pulses, the system is configured to react slowly tothe presence or absence of these pulses. At step 212, the accumulatorvalue, or number of pulses within the previous field, is compared with asecond threshold. The second threshold is associated with the number ofpulses expected to be included within a field for the copy protection tobe present. If the accumulator value for particular field is determinedto be below the second threshold, the method proceeds to step 214 wherea count value that monitors the number of fields having a sufficientnumber of pulses is decremented. If the accumulator value exceeds thesecond threshold, the count value is incremented at step 216. Thus, arunning count is maintained as to the number of fields in the inputvideo stream that include a sufficient number of AGC pulses for thepresence of copy protection to be detected.

Preferably, the count value incremented and decremented by steps 214 and216 is maintained in a counter of limited size. Thus, when copyprotection is present within an input video signal, the count value willgradually build up as fields including a sufficient number of pulses aredetected. Because the pulses are known to vary in amplitude from onefield to the other such that in some fields they will not be detected,this count will not continually increment, but will decrement when thosefields with pulses of insufficient amplitude are received. However, itis recognized that the presence of these pulses will occur in more thanhalf of the fields, and therefore, the count will increase in value overtime.

At step 218, it is determined whether or not the count value has reacheda high threshold. This comparison determines whether or not the counterhas built up to a sufficient level that it can reasonably be assumedthat copy protection is present in the input video stream. Once the highthreshold has been reached, the method proceeds to step 220 where anindication is generated that pulse type copy protection is included inthe input video signal. If the count value has not yet reached the highthreshold, the method proceeds from step 218 to step 224 where it isdetermined whether or not the count value has reached a low threshold.If the count value has reached the low threshold, an indication will begenerated at step 226 that pulse type copy protection is not included inthe input video signal. If the comparisons at step 218 and 224 are bothnegative and neither threshold has been reached either in the positivecounting direction or the negative counting direction, the method willproceed from step 224 to step 222 where the next field of the inputvideo stream is prepared for comparison with the various thresholds thatwill detect if copy protection is present.

Thus, the method of FIG. 2 steps through the input video signal on afield by field basis determining if sufficient pulses are included ineach field to surpass a threshold number of pulses that should beincluded in the frame to suggest that copy protection may be present.When this threshold is exceeded, a count value is incremented, and whenit is not, the count value is decremented. This count value is thencompared with high and low thresholds to determine if a sufficientnumber of fields have been shown to include the pulses that it isprobable that copy protection exists.

It should be noted that the first, second, high, and low thresholds maybe configured based on the particular version of pulse type copyprotection that is attempting to be detected. The high and lowthresholds are often configured such that some level of hysterisisexists between the high and low thresholds. For example, assume that aninput video signal that includes pulse type copy protection is beingreceived. The majority of the fields within the input video signal willinclude a number of pulses exceeding the second threshold such that thecount value is incremented more often than it is decremented. As thecount value builds up, it will eventually reach the high threshold. Whenthis occurs, the presence of copy protection is flagged. Eventually, thecount value will reach the maximum value of the counter, and remain nearthis value until an input signal that lacks copy protection is received.At this point, the lack of pulses in the fields within the non-copyprotected input signal will cause the count value to be decremented.Although it passes the high threshold on its downward count, the countvalue will not turn off the copy protection indication until it reachesthe low threshold.

FIG. 3 illustrates a flow diagram of a method for detecting phase flipcopy protection in an input signal, which may be used for copyprotection detection at step 104 of FIG. 1. The type of copy protectiondetected by the method of FIG. 3 includes phase flips in a portion ofthe colorburst signal that is part of each line in a display field. Thecolorburst signal is used by television sets as a reference to decodethe color to be used with each portion of the video signal. Televisionsets are typically slow to react to any phase flips included within thecolorburst portions of the input video. signal, whereas recordingdevices such as VCRs are unable to decode and record the color properlywhen such phase flips are included in the video stream.

Each line of video data includes a synchronization pulse typicallyfollowed by a colorburst signal, which is often some form of sine wave.In the phase flip copy protection technique, portions of the sine waveare flipped by a 180 degrees in phase and then reverted to theiroriginal phase at a later time. As stated earlier, recording devices aretypically incapable of dealing with these phase flips, whereastelevision sets will not react fast enough to be affected. The copyprotection technique that includes these phase flips typically includesthem in 3 or 4 sequential lines of a display field, where these sets of3 or 4 phase flip lines are typically repeated at regular intervalsthroughout the field. In order to accurately detect the type of phaseflip protection included in an input video signal, the number of lineswithin which a phase flip is included on a field by field basis shouldbe maintained, along with the interval count which indicates how manylines in a row are included in each of the phase flip groupings withineach field.

The detection method of FIG. 3 begins at step 302 where the input videosignal is demodulated to produce a demodulated chroma signal thatincludes a colorburst signal for each line of the input video signal. Atstep 304, an absolute value function is performed on the demodulatedchroma signal to produce an absolute value chroma signal that includesan absolute value colorburst signal. By taking the absolute value of thecolorburst signal, any phase flips are eliminated, as the resultingsignal is entirely positive.

At step 306, phase of the colorburst signal is compared with phase ofthe absolute value colorburst signal to determine if a phase flip hasoccurred in the current line. This may be accomplished by steps 308 and310. At step 308, the absolute value of the colorburst signal isintegrated to produce an integrated colorburst value. At step 310, theintegrated colorburst value, or some derivative thereof, is comparedwith values in the colorburst signals to determine if the phase flip hasoccurred. Integrating the colorburst signal allows for a better overallcomparison than if the absolute value colorburst signal were compareddirectly with the non absolute value colorburst signal. In oneembodiment, the integrated value is divided by two prior to comparison.

At step 312, the total number of phase flips per display field isdetermined. Thus, steps 302 through 306 detect each individual phaseflip within a field, and step 312 maintains a running count of thenumber of phase flips that occurs within each field. At step 314, theinterval number of phase flips within a field is determined. As statedearlier, the interval number of phase flips is equivalent to the numberof phase flips in each grouping of phase flips present in a field. Forexample, in a field where 40 phase flips occur, and the interval numberof phase flips is 4, there will be 10 different groupings within thefield where within each grouping there are 4 lines that include phaseflips.

By detecting the total number of phase flips and the interval number ofphase flips, these numbers can be compared with known values todetermine if this phase flip type of copy protection has been includedin an input video signal. When this type of copy protection has beenincluded, these numbers can also be used in the regeneration of the copyprotection for inclusion in output video signals.

FIG. 4 illustrates a copy protection pulse detection circuit thatincludes a pulse detector 410, an accumulator 420, a field pulsecomparator 430, a decision counter 440, and a decision comparator 450.The pulse detector 410 receives an input video signal 402 and sets apulse detect indication 417 each time a pulse that exceeds a firstthreshold is detected in the input video signal 402.

FIG. 5 illustrates a more detailed view of one embodiment of the pulsedetector 410. The pulse detector 410 includes an analog to digitalconverter (AID) 412 that receives the input video signal 402 andconverts it to a digital input signal. The digital input signal ispassed to a low pass filter 414 that filters the digital input signal toproduce a filtered input signal 404. A pulse detection comparator 405operably coupled to the low pass filter compares digital values in thefiltered input signal 404 with a first threshold, which is preferablythe vertical blanking interval peak white threshold 406. Comparison ofthe digital values with the first threshold determines whether or notthere are pulses within the input video signal 402 that exceed thethreshold, which are typically the type of pulses associated with thepulse type copy protection.

The pulse detector 410 also preferably includes a blanking interval gate416 that receives the output of the pulse detection comparator 405 andgates it with the vertical blank interval signal 408 such that pulsesare only detected during the vertical blank interval.

Returning to FIG. 4, the accumulator 420 is operably coupled to thepulse detector 410, and the accumulator 420 counts a number of pulsesdetected in each field of the input video signal to produce anaccumulated count 425. The accumulated count of the accumulator 420 ispreferably cleared by a vertical reset signal 403, which indicates thetransition between fields in the input video signal 402. The verticalreset signal 403 may correspond to the vertical-blanking intervalpresent in typical video signals.

Preferably, the accumulator 420 includes an adder 422 and a register set424 that stores the current accumulated count. The register set 424receives the vertical reset signal 403 as a clear signal, and is alsocoupled to receive the system clock signal 401. The current value storedin the accumulated count register set 424 (accumulated count 425) isprovided as an input to the adder 422 along with the pulse detect signal417.

The accumulated count 425 is provided to the field pulse comparator 430along with a second threshold 426. Preferably, the second threshold 426indicates the minimum number of pulses that should be present in aparticular field to indicate that copy protection is present in thatparticular field. The field pulse comparator 430 compares theaccumulated count 425 with the second threshold 426 such that when theaccumulated count 425 exceeds the second threshold 426, the field pulsecomparator asserts a positive count indication for the field.

The decision counter 440 is operably coupled to the field pulsecomparator 430, and, on a field by field basis, the decision counter 440will increment or decrement a decision count based on the positive countindication received from the field pulse comparator 430. If in aparticular field the field pulse comparator 430 generates a positivecount indication, the decision counter 440 will be incremented. Thus, ifenough pulses are detected within a field, the decision counter 440 willincrement. If enough pulses are not detected as indicated by the fieldpulse comparator 430, the decision counter 440 will decrement. Thedecision counter 440 is shown as an up/down counter that counts upwardswhen the field pulse comparator asserts a positive indication anddownwards for a negative indication. The decision counter 440 receivesthe clock signal 401, and is enabled by the vertical reset signal 403such that it only increments or decrements on field boundaries.

Preferably, the decision counter 440 is of limited size such that amaximum count value will eventually be achieved when an input videosignal having pulse copy protection is received. When such a signal isreceived, the decision counter 440 will begin to increment as pulses aredetected, and eventually will reach the high threshold 451. The decisioncomparator 450 will detect that the decision count has reached the highthreshold, and at this point it will set a protection pulses detectedsignal 458. This indicates that pulses have been detected and informsthe rest of the video graphics system that copy protection in the formof pulses within the input video signal 402 has been detected.Similarly, if the input video signal 402 changes and reverts to a signalthat no longer has such copy protection, the decision counter 440 willdecrement, eventually passing the high threshold 451 and reaching thelow threshold 453. When the decision count reaches the low threshold453, the decision comparator 450 will clear the protection pulsesdetected signal 458, thus indicating that copy protection in the form ofpulses is not present on the input video signal 402.

Preferably, the decision comparator 450 includes 2 comparison blocks 454and 452 that compare the decision count with the high threshold 451 andthe low threshold 453. The decision comparator 450 also preferablyincludes a set/reset flip-flop 456, where the set input of the flip-flop456 is coupled to the output of the high threshold comparator 454,whereas the reset input of the flip-flop 456 is coupled to the lowthreshold comparator 452. The flip-flop 456 also receives the systemclock signal 401. In this configuration, when the high threshold 451 isachieved by the decision count, the set input to the flip-flop 456 willbe asserted, thus bringing the protection pulses detected signal 458 toa high state. When the low threshold 453 is reached by the decisioncount, the flip-flop 456 is reset such that the protection pulsesdetected signal 458 is cleared.

Preferably, the circuit illustrated in FIG. 4 is included in a videographics integrated circuit that may be included on a video graphicscard for use in a personal computer. As such, the circuit illustrated inFIG. 4 is able to detect when pulse type copy protection is beingemployed in an input video signal, and is able to inform the remainderof the video graphics circuit of the presence of such copy protection.This enables the video graphics integrated circuit to recreate the copyprotection in any output video signal that may be recorded, as well asshut down any image capturing functions within the video graphicsintegrated circuit.

FIG. 6 illustrates a colorburst phase flip detection circuit thatincludes a phase flip detection block 510, a field counting block 520,and an interval counting block 530. The phase flip detection block 510receives a demodulated chroma signal 502 and detects when a phase flipis included in a colorburst portion of the chroma signal. The phase flipdetection block 510 checks each line of each field of the demodulatedchroma signal for phase flips. When the phase flip detection blockdetermines that a phase flip has occurred in a line, the phase flipdetection block sets a flip detected indication. The flip detectedindication is cleared based on a line boundary indication, whichpreferably includes a horizontal reset signal associated with horizontalblanking intervals typically included in video signals.

The field counting block 520 is operably coupled to the phase flipdetection block 510 and determines a field count equal to the number ofphase flips per field. The field counting block 520 determines thenumber of flips per field based on the flip detected indication from thephase flip detection block 510 and a field boundary indication.Preferably, the field boundary indication is a vertical reset signalassociated with the vertical-blanking interval that is typicallyincluded in video signals.

The interval counting block 530 is also operably coupled to the phaseflip detection block. The interval counting block determines an intervalcount equal to a number of consecutive lines having phase flips. Thus,phase flips within each field typically occur in groups of consecutivelines. The interval counting block determines the number of linesincluded in each of these groups. Thus, repeating the example discussedearlier with respect to FIG. 3, if a single display field includes 40phase flips and they are in groups of 2, the frame count will be equalto 40, whereas the interval count will be equal to 2. Each of theintervals will be spaced throughout the field.

By determining the field count and the interval count, the phase flipdetection circuit of FIG. 6 is able to indicate to other portions of avideo graphics circuit the type of phase flip copy protection includedin a particular video signal. As such, the video graphics circuit canshut down any image capturing capabilities within the video graphicscircuit when copy protection is present, and also is able to recreatethe phase flip copy protection included in the input signal on anyoutput signal that includes the data from the input signal.

The individual blocks of the phase flip detection circuit for oneembodiment are illustrated in greater detail in FIGS. 7-9. FIG. 7illustrates the phase flip detection block 510 in greater detail. Phaseflip detection block 510 receives the demodulated chroma signal 502. Anabsolute value block provides the absolute value of the demodulatedchroma signal 502 of this signal to an integrator 582. The integrator582 receives a colorburst start signal 554 that indicates the beginningof a colorburst portion of a particular line of video data. Theintegrator 582 also receives a colorburst active signal 556 that informsthe integrator 582 that the colorburst portion of the line is stillactive. The integrator 582 also receives a reset signal 558.

The integrator 582 integrates the absolute value chroma signal which isthen provided to a dividing block 584 that divides the integrated valuein half. The result of the dividing block 584 is provided to acomparator 586 along with the demodulated chroma signal 502 as receivedby the phase flip detection block 510. The comparator 586 compares theintegrated value with instantaneous values in the demodulated chromasignal 502 and detects whether or not it appears a phase flip hasoccurred. The AND gate 588 combines the output of the comparator 586 andthe colorburst active signal 556 and to produce an indication as towhether a phase flip appears to have occurred in a particular colorburstportion of a line.

An S-R flip-flop 590 is used to generate the phase flip detect signal570. When the AND gate 588 indicates that a phase flip has beendetermined within a colorburst portion of a line, the set input to theflip-flop 590 is asserted, thus setting the phase flip detect output570. Note that the flip-flop 590 is clocked by the system clock 401 andis reset on a line by line basis by the horizontal reset signal 560. Inorder to facilitate downstream circuitry within the phase flip detectioncircuit, a line pulse 572 is generated from the clock 401 and acolorburst end signal 562 that signifies when the end of the colorbursthas been reached. The line pulse signal 572 generated by the flip-flop apulse that is asserted on a line by line basis at the end of thecolorburst.

FIG. 8 illustrates a more detailed view of the field counting block 520.The field counting block 520 includes a counter 602 that is preferably a5-bit counter such that it can count between 0 and 63, where a count of63 indicates that the counter 602 is saturated. The counter 602 is resetbased on a vertical reset signal 403 such that it is cleared at the endof each field. The counter 602 is clocked by the system clock 401 andenabled by the output of an AND gate 606. The inputs to the AND gate 606include the line pulse signal 572 and the phase flip detect signal 570from the phase flip detection block 510. The other input to the AND gate606 is the output of a block 604 that determines whether or not thecounter 602 is saturated. Once per line the line pulse signal 572 willbe high. If, when the line pulse signal 572 is high, the phase flipdetect signal 570 is also high and the counter 602 is not saturated, theenable input to the counter 602 will be high, and the counter 602 willincrement.

Once per field, the register set 608 is enabled by the vertical resetsignal 403. The register set 608 receives as its input the output of thecounter 602. Thus, once per field the output of the counter 602 will beloaded into the register set 608 as the field count 522. Therefore, thefield count 522 represents the total number of phase flips detectedduring a particular field.

FIG. 9 illustrates a more detailed view of an interval counting block530 which includes a counter 702. As in FIG. 8, the counter 702 ispreferably a 5-bit counter that saturates at a value of 63. The enableinput to the counter is coupled to an AND gate 706 in the same manner asthe enable of the counter 602 of FIG. 8. Similarly, the inputs to theAND gate 706 include the phase flip detect signal 570, the line pulsesignal 572, and the output of a block 704 that indicates whether or notthe counter 702 is saturated.

The counter 702 is reset in a different manner than the counter 602. Thereset input to the counter 702 is coupled to the output of an AND gate712 that receives the inverse of the line pulse 572, the phase flipdetect signal 570, and a delayed version of the phase flip detect signal570 as its inputs. The delayed version of the phase flip detect signal570 is generated by the flip-flop 714. The reset signal of the counter702 is therefore only asserted when the end of a group of consecutivephase flips is reached. Thus, when sequential phase flips are detectedon multiple lines, the counter 702 will continue to increment until theend of the sequential run of phase flips is reached. At this point theregister set 708 will be enabled, and the output of the count 702 willbe loaded into the register set 708 as the interval count 532. Thus, theinterval count 532 determines the number of lines in a group of phaseflips.

It should be noted that the circuitry illustrated in FIGS. 4-9 are viewsof a particular embodiment. It should be apparent to one of ordinaryskill in the art that many different variations of the circuits could beimplemented which would have the same overall functionality. It shouldalso be apparent that at least a portion of the functions of thecircuitry could be implemented in software. For example, the counterscould be maintained in software.

It should be noted that each of the two different types of copyprotection described herein may be included in a particular input videostream. As such, separate circuitry may be used to detect each of thetypes of copy protection such that if either is present it can beincluded in the appropriate output signals. Thus, one or both of the twotypes of copy protection may be detected and included in the outputvideo signal.

It should be understood that the implementation of variations andmodifications of the invention and its various aspects will be apparentto those of ordinary skill in the art, and the invention is not limitedto the specific embodiments described. It is therefore contemplated tocover by the present invention any and all modifications, variations, orequivalents that fall within the spirit and scope of the basicunderlying principles disclosed and claimed herein.

1. A copy protection pulse detection circuit, comprising: a pulsedetector, wherein the pulse detector receives an input video signal andsets a pulse detect indication each time a pulse that exceeds a firstthreshold is detected in the input video signal; an accumulator operablycoupled to the pulse detector, wherein the accumulator counts a numberof pulses received in each field of the input video signal to produce anaccumulated count; a field pulse comparator operably coupled to theaccumulator, wherein the field pulse comparator compares the accumulatedcount for each field with a second threshold, wherein when theaccumulated count exceeds the second threshold for a field, the fieldpulse comparator asserts a positive count indication for the field; adecision counter operably coupled to the field pulse comparator, whereinthe decision counter increments a decision count when the positive countindication is asserted for a field and decrements the decision countwhen the positive count indication is not asserted for a field; and adecision comparator operably coupled to the decision counter, whereinwhen the decision count reaches a high threshold, the decisioncomparator sets a pulses detected indication, wherein when the decisioncount reaches a low threshold, the decision comparator clears the pulsesdetected indication.
 2. The copy protection pulse detection circuit ofclaim 1, wherein the pulse detector further comprises: an analog todigital converter that converts the input video signal to a digitalinput signal; a low pass filter operably coupled to the analog todigital converter, wherein the low pass filter filters the digital inputsignal to produce a filtered input signal; and a pulse detectioncomparator operably coupled to the low pass filter, wherein the pulsedetection comparator compares digital values in the filtered inputsignal with the first threshold, wherein the pulse detection comparatorsets the pulse detect indication each time a digital value exceeds thefirst threshold.
 3. The copy protection pulse detection circuit of claim2, wherein the pulse detector further comprises a blanking intervalgate, operably coupled to the pulse detection comparator, wherein theblanking interval gate selectively passes the pulse detect indicationbased on a received signal indicating that the input video signal is inthe vertical blanking interval.
 4. The copy protection pulse detectioncircuit of claim 3, wherein the detection circuit is included on a videographics integrated circuit.